Hot air furnace having l-shaped burners

ABSTRACT

A hot air furnace having special L-shaped gas burners extending partially into heat exchanger shells. The fuel-air mixing portions of the burners are located outside the shells in a narrow compartment such that the total depth of the furnace can be somewhat less than under conventional practice.

Apr. 4, 1972 [5 HOT AIR FURNACE HAVING L- 3,016,946 3,314,610 4/1967 Reznor...........................

'SHAPED BURNERS 126/85R 126/116RX [72] Inventor: Herbert C. McManus, Elyria, Ohio Primary Examiner chafles l Myhre [73] Assignee: American Standard Inc., New York, NY. Attorney-John E. McRae, Tennes l. Erstad and Robert G. 221 Filed: Oct. 29, 1970 Cmks ABSTRACT [2]] Appl. No.:

' A hot air furnace having special L-shaped gas burners extend- 126/91 06/116! ing partially into heat exchanger shells. The fuel-air mixing portions of the burners are located outside the shells in a narrow compartment such that the total depth of the furnace can be somewhat less than under conventional practice.

...........F24h 3/00,F24h 9/18 i26/85 R, 90 R,91 R, 110R, 126/110 B, 116 R, 116 B [52] U.S. [51] -Int. [58] Field of Search...,..............

7 Claims, 4 Drawing Figures References Cited UNITED STATES PATENTS Jaye et al. 16 R PATENTEDAPR 4 m2 3,65 3. 371

INVENTOR.

HERBERT C. M MANUS HOT AIR FURNACE HAVING L-SI-IAPED BURNERS THE DRAWINGS FIG. 1 shows a furnace constructed according to the prior art.

FIG. 2 shows a furnace constructed according to this invention. I

FIG. 3 is an enlarged view of a fuel gas burner employed in the FIG. 2 furnace.

FIG. 4 is a fragmentary sectional view on line 44 in FIG. 3.

FIG. 1 IN DETAIL FIG. 1 shows a conventional residential hot air furnace comprising a back wall 10, front wall 12, and fan deck 14 subdividing the furnace into a lower compartment 16 and an upper compartment 18. A conventional centrifugal blower 17 of the scroll-type is disposed within chamber 16 to pump room air upwardly along the outer side surfaces of individual stamped heat exchanger shells 20, formed for example as shown in U.S. Pat. No. 2,884,048 issued to H. A. Marble et al.

Each heat exchanger shell comprises a pair of mirror image stamped sections having peripheral flanges which are welded together to form a hollow rectangular shell unit. Selected edge portions of each shell section are left unconnected to form a lower opening 22 for receiving a fuel gas burner 24 and an upper opening 26 for discharge of hot combustion gases to the flue chamber 28.

Each burner 24 may be constructed as shown in U.S. Pat. No. 3,002,552 issued to J. R. Griffin; each burner may comprise a.venturi mixer duct 30 and parallel rows of flame ports in the upper face of flame tube 31. Fuel gas may be supplied to the various burners from a horizontal manifold pipe 34 having individual fuel gas spuds 36 registering with individual mixer ducts 30. Suitable air inlet openings in cap structures 38 allow air to be drawn into the individual mixer ducts for mixture with the fuel gas. The flame area designated by letter b is supplied with secondary combustion air through the enlarged opening 22, the aim being to provide complete combustion of gases within shell area 40 and discharge of fully combusted fuel through upper opening 26. The walls of each heat exchanger shell are heated by the hot gases to thereby heat the air being moved upwardly across the external surfaces of the heat exchangers by blower 17.

As shown in the drawings, each heat exchanger shell is oriented so that its longitudinal dimension is vertical and its depth dimension is horizontal (in the plane of the paper). FIG. 1 and 2 show vertical upflow units wherein room air flows upwardly in parallel flow relation to the combustion gases. The furnaces may be oriented to provide either downflow of the room air or horizontal flow, as in a ceiling type unit. The present invention, asillustrated in FIGS. 2 through 4 is believed useful in various furnace designs such as downflow, upflow or horizontal flow.

FIG. 2

The furnace of FIG. 2 is generally similar to the FIG. I furnace, and similar reference numerals are used where applicable. In the FIG. 2 construction the fuel gas burner is of a special L-shaped configuration, comprising a vertical venturi mixing tube 300 located externally of the respective heat exchanger shell 20, and a flame tube 310 extending horizontally within the respective heat exchanger shell in the direction of its depth.

It is desirable that the front compartment 42 have a width in the arrow a direction as small as possible in order to conserve on sheet metal and to minimize the front-to-rear depth of the furnace. It is also desirable that mixing tube 30 have a relatively long axial dimension to promote diffusion mixing of the gas and air particles. FIG. 1 represents a compromise between best fuel-air mixing and minimum furnace depth. FIG. 2 provides sufficient space for an elongated mixer tube while still permitting some reduction in the depth dimension of the furnace, principally compartment dimension a.

The L-shaped configuration of the FIG. 2 burner permits the longer venturi mixing tube 30a (as compared to the mixing tube 30 in FIG. 1). This is because in the FIG. 2 arrangement the burner mixing tube 30a is oriented vertically in a front compartment 42 such that the burner mixing tube can have a fairly long vertical dimension without increasing the furnace depth.

The L-shaped configuration of FIG. 2 may also be ad vantageous in enabling the burner to have a somewhat greater burner port length as denoted by dimension b. Thus, comparing FIGS. 1 and 2, it will be seen that the burner port area of FIG. 2 extends substantially the full depth of the heat exchanger shell, whereas the burner port area in FIG. 1 spans a lesser part of the heat exchanger shell depth. The longer port area of FIG. 2'provides' a more extensive heating of the shell surfaces and a more uniform wall temperature across the shell depth such that the room air slices between adjacent shell sec- BURNER CONSTRUCTION FIG. 3 shows a burner formed of two bulb-like sheet metal stampings 41 and 43 arranged in mirror image relation, with flange areas 44 thereof engaged flatwise against one another to seal the stamping joint. Welding or other joining techniques may be employed to connect the sections together as described and shown in aforementioned U.S. Pat. No. 3,002,552.

The mating burner sections form a hollow passageway 46 that defines the aforementioned venturi mixing tube 300 and the flame tube 31a. Tube 30a comprises a throat 45 for accepting fuel gas from spud 36 and air from ambient atmosphere 38, and an elongated diffusion duct 47 for mixing the air and'fuel gas together by diffusion processes. A rotary air shutter 48 may be provided on the apertured end cap 50 of the burner to control the amount of primary air drawn into the burner by the flowing fuel gas discharging out of spud 36.

In the illustrated burner the diffusion duct 47 preferably has a length c" that is at least six times the diameter of the throat 45 as measured by dimension d." This ratio of diffusion duct length to throat diameter is somewhat greater than ratios usually employed with burners of the type shown in FIG. 1, due to the aforementioned practical requirement of keeping the front-to-rear dimension of the furnace as small as possible.

The longer diffusion duct length is advantageous in enabling the duct to have a lesser angle of divergence, which provides for conversion of velocity pressure to static pressure with lesser turbulence losses. The longer duct length also may provide a more complete mixing of the air and fuel particles because each fuel particle will have a longer contact time with adjacent air particles, under conditions more closely approaching laminar flow, as distinguished from turbulent flow.

It will be seen that flame tube 31a connects with diffusion duct 47 through a curved transition duct 57 that forms a smooth continuation of the diffusion duct, thereby minimizing turbulence losses. Also, as the fuel-air mixture turns from the diffusion duct into flame tube 31a the gas passage dimension is maintained without restriction as would otherwise produce pressure loss. The aim is to maintain a satisfactory pressure in the chamber area 33 below the flame ports as will promote strong flames above the ports and minimum tendency for flashback.

The burner port structure is not part of the present invention, and has not been shown in detail. In practice the burner ports can be formed by means of a channel-like insert 54 similar to insert 11 shown in aforementioned U.S. Pat. No. 3,002,552. With such an arrangement there are provided two sets of burner slots, as at 56 and 58, said slots extending for a distance corresponding to dimension b in FIG. 2.

Prior art burners, as shown for example in FIG. 1, may sometimes have an uneven flame height from one end of the burner to the other, due principally to the fact that the burner ports near the mixing tube 30 tend to receive more fuel than the burner ports at the remote end of the burner 63. It is believed that the L-shaped burner of FIG. 3 may have an improved flame pattern due to the fact that fuel and air particles will tend to concentrate and follow along the lower guide surface 60 of the passage structure rather than short circuit along the upper surface 61 of the passage structure. The downflowing particles leaving diffusion duct 47 change direction as they move through transition duct 57 into flame tube 31a; during such directional change the inertia of the still down-flowing gas will provide a concentration of the gas particles along guide surface 60. The particles will tend to follow lower guide surfaces 60 and 62 toward the remote end 63 of the burner rather than to rebound toward the port areas adjacent surface 61. It is believed that by correctly curving surface 60 and proportioning the slope of surface 62 it may be possible 'to advantageously utilize the directional change of the gas stream between ducts '47 and 31a as a gas distribution mechanism, to thus provide a stable even flame height across the entire length of the burner dimension b. This may enable the burner to more fully occupy the depth of the heat exchanger shell, and possibly to permit a longer burner and/or a shallower exchanger shell. The burner can probably not be made to occupy the full depth of the heat exchanger shell because some space must be left for crossover lighters (not shown) from one burner to another.

The L-shaped burner preferably has the ports 56 and 58 arranged along the horizontal interior face of the L, as shown in FIG. 3 whereby the gas undergoes a 180 degree directional change between introduction to throat 45 and exit through the burner ports. The inertia effects produced by this direction reversal are believed to produce a distribution and diffusion of the air and fuel gas that will provide more complete combustion and uniform flame height along the burner length dimension b.

It will be noted that the furnace of FIG. 2 has a front-to-rear dimension that is somewhat less than the corresponding dimension of the FIG. 1 burner. In practice the FIG. 1 furnace might have a depth of about 28 inches. It is believed that by employing the concept of the present invention it might be possible to reduce the depth of the furnace by perhaps 3 or 4 inches. A principal part of the dimension reduction would be in the front compartment 42; thus it might be possible to reduce dimension a from about 9 inches down to about 6 inches. The remaining depth reduction would be in a reduced depth dimension of the heat exchanger shells. It is contemplated that even though the heat exchanger shells might be reduced in size the heat transfer capability of the furnace would not be reduced because the flame coverage across the shell interior would be better. By using the L-shaped burner it is believed possible to achieve furnace depth reduction without adding any height to the furnace. This is because the L-shaped burner of FIG. 2 has about the same vertical dimension as the straight burner of FIG. 1 at those points where the burner is within the heat exchanger.

I claim:

1. A furnace comprising parallel hollow heat exchanger shells having longitudinal dimensions and depth dimensions, each shell having a burner reception opening in one of its longitudinal edges; a fuel gas supply means external to the heat exchanger shells; and individual ribbon type gas burners extending into the heat exchanger shells through the burner openings; each burner being of L-shaped configuration, comprising a venturi mixing tube extending longitudinally of the respective shell along the shell exterior to receive fuel gas from the supply means, and a flame tube extending within the respective shell along its depth dimension to discharge flames generally parallel to the longitudinal dimension of the shell.

2. The furnace of claim 1 wherein each venturi mixing tube comprises a throat for accepting fuel gas from the supply means and air from the ambient atmosphere, and an elongated divergent diffusion duct extending from the throat.

3. The furnace of claim 2 wherein each diffusion duct has a length that is at least six times the diameter of the throat.

. The furnace of claim 2 wherein each flame tube has a first longitudinal wall having a row of burner ports therealong, and

a second longitudinal gas-guide wall of sloping character facing the burner ports for directing gas thereto, said gas-guide wall being joined to one wall of the diffusion duct by a smoothly curving transition wall that redirects the gas from the diffusion duct into the flame tube with minimum turbulence.

5. The furnace of claim 4 wherein said gas-guide wall slopes toward the burner ports as it moves toward the downstream end of the burner.

6. The furnace of claim I wherein the flame tube has a row of burner ports arranged along an interior face of the L, whereby the gas undergoes a directional change between introduction to the burner mixing tube and exit through the burner ports.

7. The furnace of claim 1 wherein the burner ports extend very close to the juncture between the two legs of the L, whereby the combustible gases are required to make a very sharp turn to reach the ports nearest said juncture. 

1. A furnace comprising parallel hollow heat exchanger shells having longitudinal dimensions and depth dimensions, each shell having a burner reception opening in one of its longitudinal edges; a fuel gas supply means external to the heat exchanger shells; and individual ribbon type gas burners extending into the heat exchanger shells through the burner openings; each burner being of L-shaped configuration, comprising a venturi mixing tube extending longitudinally of the respective shell along the shell exterior to receive fuel gas from the supply means, and a flame tube extending within the respective shell along its depth dimension to discharge flames generally parallel to the longitudinal dimension of the shell.
 2. The furnace of claim 1 wherein each venturi mixing tube comprises a throat for accepting fuel gas from the supply means and air from the ambient atmosphere, and an elongated divergent diffusion duct extending from the throat.
 3. The furnace of claim 2 wherein each diffusion duct has a length that is at least six times the diameter of the throat.
 4. The furnace of claim 2 wherein each flame tube has a first longitudinal wall having a row of burner ports therealong, and a second longitudinal gas-guide wall of sloping character facing the burner ports for directing gas thereto, said gas-guide wall being joined to one wall of the diffusion duct by a smoothly curving transition wall that redirects the gas from the diffusion duct into the flame tube with minimum turbulence.
 5. The furnace of claim 4 wherein said gas-guide wall slopes toward the burner ports as it moves toward the downstream end of the burner.
 6. The furnace of claim 1 wherein the flame tube has a row of burner ports arranged along an interior face of the L, whereby the gas undergoes a 180* directional change between introduction to the burner mixing tube and exit through the burner ports.
 7. The furnace of claim 1 wherein the burner ports extend very close to the juncture between the two legs of the L, whereby the combustible gases are required to make a very sharp turn to reach the ports nearest said juncture. 